No one has ever paid more attention to the streets and sidewalks of New York City than William H. Whyte. In 1969, Whyte—the author of the sociological classic The Organization Man—got a grant to run what came to be known as the Street Life Project, and spent much of the next sixteen years simply watching what New Yorkers did as they moved through the city. Using time-lapse cameras and notebooks, Whyte and his group of young research assistants compiled a remarkable archive of material that helped explain how people used parks, how they walked on busy sidewalks, and how they handled heavy traffic. Whyte’s work, which was eventually published in his book City was full of fascinating ideas about architecture, urban design, and the importance to a city of keeping street life vibrant, it was also a paean to the urban pedestrian. “The pedestrian is a social being,” Whyte wrote. “He is also a transportation unit, and a marvelously complex and efficient one.” Pedestrians, Whyte showed, were able, even on crowded sidewalks, to move surprisingly fast without colliding with their neigh- hors, in fact, they were often at their best when the crowds were at their biggest. “The good pedestrian,” Whyte wrote, “usually walks slightly to one side, so that he is looking over the shoulder of the person ahead. In this position he has the maximum choice and the person ahead is in a sense running interference for him.”

New Yorkers mastered arts like “the simple pass,” which involved slowing ever so slightly in order to avoid a collision with an oncoming pedestrian. They platooned at crosswalks as a protection against traffic. In general, Whyte Wrote, “They walk fast and they walk adroitly. They give and they take, at once aggressive and accommodating. With the subtlest of motions they signal their intentions to one another.” The result was that “At eye level, the scene comes alive with movement and color—people walking quickly, walking slowly, skipping up steps, weaving in and out in crossing patterns, accelerating and retarding to match the moves of others. There is a beauty that is beguiling to watch.”

What Whyte saw—and made us see—was the beauty of a well-coordinated crowd, in which lots of small, subtle adjustments in pace and stride and direction add up to a relatively smooth and efficient flow. Pedestrians are constantly anticipating each other’s behavior. No one tells them where or when or how to walk. 1nead, they all decide for themselves what they’ll do based on their best guess of what everyone else will do. And somehow it usually works out well. There is a kind of collective genius at here.

It is, though, a different kind of genius from the one represented by the NFL point spread or Google. The problem that a crowd of pedestrians is “solving” is fundamentally different from a problem like “Who will win the Giants—Rams game, and by how much?” The pedestrian problem is an example of what are usually called coordination problems. Coordination problems are ubiquitous in everyday life. What time should you leave for work? Where do we want to eat tonight? How do we meet our friends? How do we allocate seats on the subway? These are all coordination problems. So, too, are many of the fundamental questions that any economic system has to answer: Who will work where? How much should my Factory produce? How can we make sure that people get the goods and that to solve it, a person has to think not only about what he believes the right answer is but also about what other people think the right answer is. And that’s because what each person does affects and depends on what everyone else will do, and vice versa.

One obvious way of coordinating people’s actions is via authority or coercion. An army goose-stepping in a parade is, after all, very well-coordinated. So, too, are the movements of workers on an old-fashioned assembly line. But in a liberal society, authority (which includes laws or formal rules) has only limited reach over the dealings of private citizens, and that seems to be how most Americans like it. As a result many coordination problems require bottom-up, not top-down, solutions. And at the heart of all of them is the same question: How can people voluntarily—that is, without anyone telling them what to do—make their actions fit together in an efficient and orderly way?

It’s a question without an easy answer, though this does not mean that no answer exists. What is true is that coordination problems are less amenable to clear, definitive solutions than are many of the problems we’ve already considered. Answers, when they can be found, are often good rather than optimal. And those answers also often involve institutions, norms, and history, factors that both shape a crowd’s behavior and are also shaped by it. When it comes to coordination problems, independent decision making (that is, decision making which doesn’t take the opinions of others into account)’ is pointless—since what I’m willing to do depends on what I think you’re going to do, and vice versa. As a result, there’s no guarantee that groups will come up with smart solutions. What’s striking, though, is just how often they do.